Contact arm for self-resetting magnetic contact relays



Jan. 17, 1950 A. H. LAMB 2,494,622

CONTACT ARM FOR SELF-RESETTING MAGNETIC CONTACT RELAYS 2 Sheets-Sheet l Filed Feb. 6, 1948 Jan. 17, 1950 A. H. LAMB 2,494,522

CONTACT ARM FOR SELF-RESETTING MAGNETIC CONTACT RELAYS Filed Feb. 6, 1948 2 Sheets-Sheet 2 WW/WWW W Patented Jan. 17, 1950 UNITED STATES PATENT OFFICE CONTACT ARM FOR SELF-RESETTING MAGNETIC CONTACT RELAYS Application February 6, 1948, Serial No. 6,777

9 Claims.

This invention relates in general to highly sensitive instrument relays'of the magnetic contact type, and inparticular to those in which the contacts are separated, i. e. reset, by the application of a countertorque to the moving system. *As shown in my prior United States Patent No. 2,346,589;'issued April 11, 1944, such a counter torque may be'obtained in a single coil instrument'by-passing a relatively high'resetting curient'puls'e through the moving coil in a direction opposlteto that traversed by the control current; or by providing one coil for the control current and 'a separate one for the resetting current. In either case, the resetting current is maintained until the counter torque developed thereby is sufficient to overcome the forces of magnetic attraction between the contacts whereupon the contacts separate and likewise openthe resetting current circuit. '-Toassurea reliable non-chattering engagementbetwe'en the twogcontact members, the magnetic forces of attraction between them should be as high as possible but the upper limit of this force is'determined by the maximum a1- lo'wable magnitude of the resetting current and the period during which it may be safely applied to the delicate coil'without overheating the latter. Thus in designing the instrument, a magnetic attractive force factor is chosen which will be sufiicient to hold the contacts firmly together but which will nevertheless be certain to be overcome by the counter torque developed by the resetting current within a comparatively brief period. I In the case of a single coil instrument for example Where both the control-current and the temporary resetting current traverse the same winding, and'the instrument is designed for a continuous controlcurrent input'of the order of several microamperes, it has been the practicein thei'ndustry to use a resetting current of a substantiallyhigher order of a few milliamperes in order to effect contact separation.

So long asthe mutually engaging surfaces of thecontact members remain smooth, satisfactory operation ofthe relay canbe expected. However, experience has shown that even with currents in the milliampere range, contact arcing cannot always be avoided and this quite often causes the surfaces of the contacts to pit. -Pitting of the contacts causes them to stick and thus adds an additional attractive force which-mustbe overcome by the counter torque developed .byv the reset current. While this is taken into consideration in designing a partied!ar instrument, so that the developed counter torque will be sufficient despite a limited amount of contact sticking to effect a separation of the contacts within the calculated period during which the reset current'can be safely applied without fear of coil damage, it is quite possible especially when the contacts become deeply pitted, that the reset current period will be unduly prolonged with the result that the coil then becomes overheated to such extent that the insulation on the winding' is damaged.

The general object of this invention is to pro vide'an improved construction for the moving system of sensitive relay instruments of the class described which will always assure a positive and quick separation of the magnetically attracted contacts to the end that the reset current period willbe certain never to exceed the maximum for which the instrument is designed.

In general, the objective is attained by a novel structural arrangement of the pointer element which permits the moving system to quickly gain an initial angular momentum in the contact separating direction, which momentum is then applied suddenly as a contact separating force as distinguished from the present conventional practice of increasing the contact separating force gradually from the instant that the reset current is applied which results in a slow and not always effective start of the moving system.

In one form of the invention, the moving system of the instrument includes a relatively flexible pointer which carries the movable contact near the outer end, and an auxiliary and relatively stiff arm which, after gaining an initial momentum with the moving system, functions to strike a sudden hammer blow against the flexible pointer close to the movable contact.

In another form of the invention, a single relatively stiff pointer element is used, but the pointer shaft includes a highly flexible section near its outer end adjacent the movable contact which permits the inner end of the pointer shaft and the remainder of the moving system to gain an initial momentum in the contact separating direction before the contact separating force is suddenly applied to the outer portion carrying the contact.

' In yet another form of the invention, the structural features of both of the above mentioned embodiments are combined to bring about a separation of the contacts.

In the accompanying drawings, Fig. 1 is a view in front elevation illustrating the first referred to form of the invention as applied to an instrument relay of the single coil type, togethe with the circuit arrangement illustrated in Fig. 1 of my prior United States Patent No. 2,346,589; Fig. 2 is a side elevation as viewed from the right in Fig. 1; Fig. 3 is a horizontal section taken on line S3 of Fig. 2

Fig. l is a similar sectional view illustrating a modified construction for the outer end of the reset arm; and Fig. 5 is a view similar to Fig. 1 illustrating the positions taken by the pointer and reset arm shortly after the reset currenthas been applied to the coil.

Figs. 6, '7 and 8 are front elevations of a modified form of the invention featuring .a single pointer element including a flexible helical coil section adjacent the movable contact member, and which show, in sequence, the behavior of the pointer during the contact separating phase of the relay system;

Fig. 9 is a fragmentary elevation of another pointer arrangement similar to that .shown in Figs. 6, 7, 3 but in which the flexible portion at the outer end of the pointer is constituted by a straight shaft section of reduced dimension.

Figs. 10, 11 and 12 are front elevations showing in sequence the mode of operation of yet another embodiment or" the invention which, in general, combines the features of the pointer construction of Figs. l-5 with that of Figs. 6-8.

Reierring now to Figs. 1-5, the instrument relay is seen to be of the well known direct current type including a pivoted coil l rotatable in the air gap of a permanent magnet 2 and which is connected to a variable control current source 3 that develops only .a small current flow through the coil 1!, for example, of the order of a few micro amperes.

For purposes of illustration, current source 3 is shown diagrammatically as a thermocouple but it is to be understood that such source may be a photoelectric cell, a potentiometer, or the potential drop across a temperature-variant resistance, according to the character of the factor or quantity being measured.

A pointer rotated by .coil I carries at its outer end a small rider or contact 5 of magnetic material for cooperation with a relatively stationary magnetic contact The magnetized contact ,6 is so positioned that contact 5 is drawn into ongagement with it when pointer 4 has rotated in a clockwise direction to a predetermined graduation on the scale I by the flow of the control current through coil '1. A load circuit including a current source 8 and a load device 9 is connected between the relay contacts 5, 5. The load device 9 may he a visual or an audible signal, a motor, or a power relay according to the desired control or relay action. Furthermore, in some cases, it may be desirable to use magnetized material for the movable contact member 5 and magnetic material for the stationary .contact 6.

The resetting curreent may be drawn from the power source 8 of the load circuit by shunting the relay coil l across the load device 9, a resistor 50 being included in the coil branch of this parallel circuit network to limit the resetting current fiow to a magnitude that will not damage the coil l, assuming of course that the current is not applied for too long a period. In general, as previously explained, the resetting current may be of the order of a few milliamperes when the relay is designed for a continuous control current input of the order of several microamperes. The control current source 3 is in shunt with coil I so far as concerns current flow from the power source 8, and a current limiting resistor I l is placed in series with source 3 to restrict the flow of power current through the source 3.

An engagement of the magnetic rela contacts 5,, 6 closes the load circuit to energize the load device 9 from the battery 8, and .also completes the resetting circuit through the resistor l6 and coil I. The polarity and magnitude of the resetting current vflow through the instrument coil 1 are such that the coil rotates counter-clockwise. When relay contacts 5, 6 open, the load circuit is opened as is also the resetting current circuit. Assuming that the contacts separate quickly, the flow of the resetting circuit is thus limited to .a relatively short period, and, even though it be of a value appreciably higher than the control current, no damage to the coil i will result.

Thus it will be seen that the particular relay circuit described is of the pulsing or periodic closing type as the energization of the load device 9 and the resetting of the relay moving system is designed to take place alternately so long as the current output of the control current source .3 is within the range corresponding to a closure of the relay contacts 5, 6.

The elements of the instrument relay so far introduced and the circuit controlled thereby are all well known and :are described in my previously issued Patent No. 2,346,589.

This application is directed to an improved structural arrangement of the pointer and movable contact carried thereby which will assiu'e quick and positive separation of the rela contacts 5, 6 even under extremely adverse conditions to the end that the resetting current pulse will not be unduly prolonged.

As previously explained, the objective is attained by providing a pointer construction such as will permit the moving system to gain an initial momentum in the contact resetting direction upon the application of the resetting current to the coil thus developing a relatively high order of potential energy which is applied suddenly at a point close to the contacts, as distinguished from the present conventional practice of applying the counter, contact separating force through the pointer from the instant that the resetting current is applied to the coil which gives rise to a rather slow and far less effective start of the moving system.

As shown in Figs. 1-5, pointer 4 carrying the contact 5 is made quite thin and relatively flexible so as to impose a negligible amount of restraining force on coil I as the latter initiates its motion in the contact resetting direction. The pointer may be mounted separately on the coil staff 12 or, as illustrated, can be attached such as by spot welding to a radially aligned reset arm I3 that is mounted upon staff l2 for rotation with the coil. Arm I3 is relatively stiff as compared with pointer 4 and the attachment between the two is confined to an area immediately adjacent the staff end by bending arm 43 slightly in a direction normal to the plane of pointer rotation for the purpose of permitting pointer 4 to undergo an initial and comparatively unrestrained deflection throughout substantially its entire length when the resetting current is first applied. Mutually perpendicular extensions 13a on arm 13 are provided and these carry the usual adjustable weights M for balaneing the moving system,

The outer end of reset arm l3 terminates in a striker l3b extending generally parallelto the coil axis intothe plane of movement of pointer 4 so as to strike thelatte'r a sudden blow at a point immediately below contact member 5. Although a short straight rod section would be satisfactory as a striker, I prefer that it be given a curvature concave in the direction of pointer 4 so as to partially encircle the latter as shown clearly in Fig. 3 and thereby prevent the striker from sliding past the pointer upon striking it.

If desired, the striker may be modified as indieated at l3c in Fig. 4 to completely encircle the pointer shaft 4.

Now when the resetting current is first applied to coil l, the latter and arm' l3 will rotate for a few degrees in a counter clockwise direction and acquire an appreciable angular momentum practically unimpeded by any counter torque acting through the pointer shaft 4 which flexes freely as shown in Fig. 5. The outer end of pointer 4 which in the meantime has remained practically stationary is now struck a comparatively hard andsudden blow by striker I3b quickly forcing the pointer carried contact 5 away from stationary contact 6. y

' -Byso transferring the point of application of the contact separating force from the coil axis radially to a point immediately adjacent the contact member and, in addition, permitting the moving system including the reset arm to acquire an appreciable angular momentum, it should now be evident that a far more eflicient use is made of the counter contact-reset torque than has been possible heretofore.

In the embodiment shown in Figs. 6-8 the auxiliary striker arm is omitted and the pointer shaft I5, which is relatively stiff 'as compared with pointer 4 of the previously described construction, is provided with a flexible helical coil section 150: located comparatively close to the movable contact IS. The upper and lower ends of coil l5a preferably include a few tight turnsl5b forfirm attachment to the upper andlower pointer sections I50, l5d but other modes of attachment can of course be employed The function of the flexible coil section Ilia as with the Fig. 1 construction is to allow the moving system to gain an initial angular momentum, the potential energy of which is thenapplied suddenly as a contact separating force. close to the contacts.

When the resetting current pulse is initially applied .to coill, the helical section I5a will at first yield quite freely in the plane of movement of pointer shaft [5 and move to the position shown in Fig. '7. The initial deformation of the helical pointer section l5a will cause the outer end of the pointer and contact member it to turn and slide downwardly at an angle with respect to the rounded magnetized contact member I! but the force required for this is negligible compared with that required to finally overcome the attracting magnetic forces and hence the lower section l5d of the pointer and the remainder of the moving system will gain an appreciable momentum in the contact reset direction during the initial movement of the assembly from the position shown in Fig. 6 to that shown in Fig. '7. As the parts reach the Fig. '7 position, however, the resistance of helical section a to deformation undergoes a rather abrupt increase with the result that section [5a stiffens materially and the potential counter torque of the moving system is transmitted suddenly through it to contact member H5,

as shown in Fig. 8 causing it to pull quickly and with comparatively great force away from the magnetized contact member II.

If desired, the flexible helical section l5a of Fig. 6 can be replaced with a short straight pointer section l8a, as shown in Fig. 9, the section being appropriately reduced in areal dimensions as compared with the area of the lower and upper pointer sections [80, I81) so as to give it the necessary degree of flexibility in the plane of pointer motion and thus permit the moving system to gain the essential initial momentum.

Figs. 10-12 illustrate still a third form of the invention that may be said to combine the basic features of the two previously described embodiments. Here, pointer 19, made of relatively stifi material, is seen to be interrupted at a point immediately below the movable contact member 2| The lower end of the upper pointer section [9b carrying contact member 20 is secured at 22 to the upper end of a helical coil 23 made from a material more flexible than that from which pointer i8 is made. Coil 23 which surrounds an appreciable portion of the lower pointer section 1.90 below the point-of-break lScl is of such diameter as to permit a considerable lateral movement therein ofthe pointer section 190, and the lower end of the coil is secured at 24 to the latter.

When the resetting current pulse is first applied to coil l, coil 23 yields quite freely as in the case of the construction shown in Figs. 6-8, this being accompanied by a slight turning and sliding movement of contact 29 with respect to the stationary magnetized contact 2|, and thus permits the lower pointer section I and th remainder of the moving system to gain an initial angular momentum in the contact reset direction prior to reaching the position shown in Fig. 11. When the latter position is reached the upper end of the lower pointer section I90 strikes against the side of the coil 23 giving it a sudden and hard blow as shown in Fig. 12 which is then most effective to quickly overcome the magnetic attractive force between contacts 20, 2| as well .as any additional contact attractive forces which may arise as a result of contact pitting.

In conclusion, I wish it to be understood that while several different embodiments of the invention have been described and illustrated, still other modifications may be adopted b those skilled inthe art without departing from the spirit and scope of the inventiveprinciples as .defined in the appended claims.

' vJlrclaim:

1. In an instrument type relay, a moving sysftem including rotatable coil means adapted to be connected to a source of control current, contact arm means rotatable with said coil, a stationary contact, a movable contact carried by said arm means for engagement with said stationary contact, one of said contacts being of magnetic material and the other of magnetized material to assure firm engagement therebetween, means for applying a counter torque to said moving system to develop a force for resetting said contacts, and means associated with said contact arm means for suddenly applying said force to said contact arm means at a point close to said movable contact subsequent to an initial and substantially unrestrained angular deflection of said moving system in said contact reset direction.

2. In an instrument type relay, a moving system including rotatable coil means adapted to be connected to a source of control current, contact arm means rotatable with said coil, a sta- 'tionary contact, a movable contact carried by said arm means for engagement with said stationary contact, one of said contacts being of magnetic material and the other of magnetized material to secure firm engagement therebetween, means developing a momentum in said movingsystem in the contact reset direction, and means converting said momentum into an impact force against said contact arm means in the reset direction subsequent to an initial and substantially unrestrained angular deflection of said moving system in said contact reset direction.

3. In an instrument type relay, a moving system including rotatable coil means adapted to be connected to a source of control current, contact arm means rotatable with said coil, a stationary contact, a contact carried by said arm means for engagement with said stationary con tact, one of said contacts being of magnetic material and the other of magnetized material to assure firm engagement therebetween, resetting means rotatable with said contact arm means effective to permit said moving system to gain an initial and substantially unrestrained angular momentum in the contact reset direction upon the application of a counter torque to said system while said contacts remain engaged and thereafter to apply a contact separating force to said movable contact, and means for developing said counter torque.

4. In an instrument type relay, a moving system including rotatable coil means adapted to be connected to a source of control current, a contact arm rotatable with said coil, a stationary contact, a contact carried by said arm for engagement with said stationary contact, one of said contacts being of magnetic material and the other of magnetized material to assure firm eng-agement therebetween, said arm being relatively flexible in the plane of movement thereof to permit said moving system to gain an initial angular momentum in the contact reset direction upon the application of a counter torque to said system, means for developing said counter torque, and a relatively stiff reset arm rotatable with said coil, said reset arm including a striker element disposed in the plane of movement of said contact arm and spaced therefrom for imparting to said contact arm a sudden blow close to said movable contact following a predetermined angular travel of said moving system in the com tact reset direction.

5. An instrument relay as defined in claim 4 wherein said striker partially surrounds said contact arm.

6. An instrument relay as defined in claim 4 wherein said striker completely surrounds said contact arm.

'7. In an instrument type relay, a moving system including rotatable coil means adapted to be connected to a source of control current, a contact arm rotatable with said coil, a stationary contact, a contact carried by said arm for em gagement with said stationary contact, one of said contacts being of magnetic material and the other of magnetized material to assure firm engagement therebteween, said arm being relatively stiff except fora section thereof adjacent said movable contact and which section is relatively flexible in the plane of movement of said arm to permit said moving system to gain a substantially unrestrained initial momentum in the contact reset direction upon an application of a counter torque to said moving system, and means for developing said counter torque.

8. An instrument type relay asdefined in claim 7 wherein said flexible section is constituted by a helical coil.

9. In an instrument type relay, a moving system including rotatable coil means adapted to be connected to a source of control current, a contact arm rotatable with said coil, a stationary contact, a contact carried by said arm for engagement with said stationary contact, one of said contacts being of magnetic material and the other of magnetized material to assure firm engagement therebetween, said arm being relatively stiff and divided axially into upper and lower sections at a point close to said movable contact, a relatively flexible helical coil interconnecting said upper and lower arm sections and which functions to permit said lower arm section and the remainder of said moving system to gain an initial angular momentum in the contact reset direction upon the application of a counter torque to said system, said coil also surrounding a portion of said lower arm section be low its upper end and being spaced radially therefrom to permit an initial relative motion therebetween during the reset motion, and means for developing said counter torque.

ANTHONY H. LAMB.

REFERENCES CITED The following references are of record in the 

